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Platelets

Does this test have other names?

Platelet count, thrombocyte count

What is this test?

This test measures the number of platelet cells in your blood.

Platelets are disk-shaped cells that help your blood form clots. Platelets are also called thrombocytes. They are made in the spongy center of bones, called the bone marrow. About two-thirds of your platelets circulate in your blood all the time. They live for about seven days.

The number of platelets in your blood can give your doctor valuable information about how well your blood clots to stop bleeding, how well your bone marrow is working, and about diseases that affect your platelet count.

Why do I need this test?

You may need this test as part of routine blood testing during a physical exam. You may also need this blood test if you have signs or symptoms that you may have too many or too few platelets.

Having too many platelets is called thrombocythemia or thrombocytosis. Signs and symptoms may include:

  • Weakness

  • Bleeding

  • Headache and dizziness

  • Numbness and burning of hands and feet

Having too few platelets is called thrombocytopenia. Signs and symptoms may include:

  • Red or brown bruising of the skin, a condition called purpura

  • Small red dots on the skin, a condition called petechiae

  • Nosebleeds

  • Mouth bleeding

  • Blood in bowel movements

You may also have this test if a blood test called a peripheral smear shows an abnormal platelet count.

What other tests might I have along with this test?

Your doctor may also order a complete blood count, or CBC, which measures all the cells in your blood.

Your doctor may also order a mean platelet volume (MPV). MPV tells your doctor about the size of your platelets. You may also need blood tests to look at your blood's ability to form blood clots, called a coagulation profile.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Platelets are measured as the number of platelets found in 1 microliter of blood. This is what the numbers may mean:

  • 150,000 to 450,000 platelets is normal

  • Fewer than 150,000 platelets is low

  • Fewer than 50,000 may cause mild bleeding

  • Fewer than 20,000 may cause serious bleeding

Some common causes of an abnormally high number of platelets include:

  • Blood cell cancers like leukemia, lymphoma, and Hodgkin disease

  • Other cancers

  • Kidney failure

  • Inflammatory disease like rheumatoid arthritis

  • Certain types of anemia

  • Active infections

Some common causes of an abnormally low number of platelets include:

  • Certain types of anemia

  • Infections

  • Heart failure

  • Cancer treatment

  • Bone marrow cancers

  • Alcohol abuse

  • Bleeding

  • Certain inherited syndromes

  • Liver or kidney disease

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Your platelet count may go up if you live at a high altitude or have recently exercised strenuously. Your platelet count may go down if you are about to have a menstrual period, are pregnant, or are taking birth control pills.

Certain drugs can also affect your platelet count.

How do I get ready for this test?

You should avoid strenuous exercise before the test. If you are a woman, let your doctor know if you may be pregnant or are having your period. Also be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.